Spray forming is a unique solidification process in which metal melt is atomised by inert gas into droplets of 10-200 microns in size, flying at subsonic speed onto a deposition substrate. During the flight the droplets are rapidly cooled with a cooling rate between 100 to 100,000 degrees per second in a controlled way so that the solidification of the metal is not dependent on the temperature and/or the thermal properties of the deposition surface like a mould. The particles arriving at the mould are in such a condition that welding to the already deposited metal is complete and no interparticle boundaries are developed. As a result, high-quality materials are made with fine, equiaxed and homogeneous microstructures. These features are especially prominent in making high-alloy metal components like for example die inserts and tooling heads.
Such components often need cooling for proper operation and for preventing overheating shortening the component lifetime and possibly leading to damages. Traditionally cooling channels have been made by machining. However, drilling the channels into usually very hard spray formed material is troublesome and time consuming. There have also been practices to form the cooling channels already during the spray forming process by setting metal tubes on the deposited material at an intermediate stage of the process. After subsequent deposition to the final thickness of the structure, the tubes form open channels within the component.
There are, however, many problems in this approach. At first, the tubes create a shadowing effect which prevents deposition of sprayed metal below them. This leads to empty gaps formed below the tubes in the areas where the spray can't fall, which in turn impairs the cooling efficiency and often causes stresses, distorting or even cracking of the component. In addition, the upper surface of the sprayed material usually follows the profile of the deposition substrate. In contrast, the metal tubes to be placed on this kind of surface are rigid. Thus, the more there are vertical changes in that surface the more there are cavities around the tube decreasing the cooling efficiency.